1. Field of the Invention
This invention relates to a fine pattern, and more particularly to a method of forming a fine pattern, a liquid crystal display device having a fine pattern and a fabricating method thereof.
2. Description of the Related Art
In general, a liquid crystal display (LCD) device controls light transmittance of a liquid crystal having dielectric anisotropy using an electric field, to thereby display a picture. The LCD device includes a liquid crystal display panel for displaying a picture with a liquid crystal cell matrix, and a driving circuit for driving the liquid crystal display panel. A switching device is formed in each of the cell areas in the liquid crystal matrix. An LCD device is used as a display in televisions, computer monitors, office equipment, and cellular phones.
FIG. 1 is a schematic perspective view showing a structure of a related art liquid crystal display panel. Referring to FIG. 1, the related art liquid crystal display panel includes a color filter substrate 10 and the thin film transistor substrate 20 that are attached to each other with liquid crystal molecules 24 therebetween. The liquid crystal molecules 24 are long and thin.
The color filter substrate 10 includes a black matrix 4, a color filter 6 and a common electrode 8 that are sequentially provided on an upper glass substrate 2. The black matrix 4 is provided on the upper glass substrate 2. The black matrix 4 defines cell areas on the upper glass substrate 2 into a plurality of cell areas that are later provided with color filters 6, and prevents light interference between adjacent cell areas and reflection of external light. The color filters 6 are provided in the cell areas defined by the black matrix 4 in such a manner as to have red (R), green (G) and blue (B) color filters, thereby transmitting red, green and blue lights. The common electrode 8 is formed of a transparent conductive layer coated over the color filter 6. The common electrode 8 supplies a common voltage Vcom that serves as a reference voltage during the driving of the liquid crystal molecules 24. Further, an over-coat layer (not shown) for providing a smooth surface above the color filter 6 may be provided between the color filter 6 and the common electrode 8.
The thin film transistor substrate 20 includes a pixel electrode 22 for each cell area on a lower glass substrate 12 and a thin film transistor 18 at each crossing of a gate line 14 and a data line 16 for each cell area on the lower glass substrate 12. The thin film transistor 18 applies a data signal from the data line 16 to the pixel electrode 22 in response to a gate signal from the gate line 14. The pixel electrode 22 is formed of a transparent conductive layer that receives a data signal from the thin film transistor 18 to drive the liquid crystal molecules 24.
The liquid crystal molecules 24 have a dielectric anisotropy and thus are rotated in accordance with an electric field generated by a data signal from a pixel electrode 22 and a common voltage Vcom from the common electrode 8 to control light transmittance through the liquid crystal molecules 24. Different electric field potentials implement different levels of gray scale. Further, the liquid crystal display panel includes an alignment film for initially aligning the liquid molecules 24, and a spacer (not shown) for maintaining a cell gap between the color filter substrate 10 and the thin film transistor substrate 20.
The color filter substrate 10 and the thin film transistor substrate 20 of a liquid crystal display panel are formed by a plurality of mask processes. Each mask process includes a plurality of sub-processes, such as thin film deposition (coating), cleaning, photolithography, etching, photo-resist stripping and inspection processes. Since the thin film transistor substrate is manufactured by a semiconductor process and a plurality of mask processes, fabrication processes are major cost in the manufacture of a liquid crystal display panel. Therefore, a manufacturing process for the thin film transistor substrate has been developed to reduce the number of mask processes from the five-round mask processes that are the standard number of mask processes for fabricating a thin film transistor substrate.
Liquid crystal display devices can be classified as either a vertical electric field type in which a vertical direction electric field extends between the color filter and the thin film transistor substrates or a horizontal electric field type is which a horizontal direction electric field extends across the surface of one of the two substrates. The vertical electric field type liquid crystal display device can drive a liquid crystal of TN (twisted nematic) mode with a vertical electric field between a common electrode on an upper substrate and a pixel electrode on a lower substrate. The vertical electric field type liquid crystal display device has an advantage in that the aperture ratio is high, but on the other hand, it has a disadvantage in that the viewing angle is narrow, about 90°.
The horizontal electric field type liquid crystal display device drives a liquid crystal of IPS (in-plane switch) mode with a horizontal electric field between a pixel electrode and a common electrode, which are formed in parallel on the thin film transistor substrate. The horizontal electric field type liquid crystal display device has an advantage in that the viewing angle is wide, about 160°, but on the other hand, it has a disadvantage in that the aperture ratio is low. In the liquid crystal display device of horizontal electric field applying type, the pixel electrode and the common electrode are formed of a plurality of finger in each cell area, so that the liquid crystal display device of horizontal electric field applying type has a drawback of a small aperture ratio. A line width of the pixel electrode and the common electrode must be decreased to increase the aperture ratio, but the line width is limited by an exposure resolution of the photolithography process.
FIG. 2A to FIG. 2C are cross-sectional views showing a method of forming a related art electrode. As shown in FIG. 2A, a conductive layer 42 is formed on a substrate 40, and a photo-resist pattern 44 is formed on the conductive layer 42. The photo-resist pattern 44 is formed by a development process and a firing process after a pattern of a mask is transposed onto a photo-resist by an exposure process. The minimum line width of the photo-resist pattern 44 can not be narrower than the exposure resolution of an exposure apparatus. For example, when a photo resolution of a scan type exposure apparatus is approximately 4 μm, the minimum line width of the photo-resist pattern 44 can not be much narrower than 4 μm.
Referring to FIGS. 2B and 2C, the conductive layer 42 is etched by an etching process, thereby providing an electrode 46 overlapped by the photo-resist pattern 44, and then the photo-resist pattern 44 is removed by a stripping process. In this case, the conductive layer 42 is over-etched due to the characteristics of a wet-etching process so that the electrode 46 has a narrower line width than the photo-resist pattern 44. However, when the minimum line width of the photo-resist pattern 44 is about 4 μm, the line width of the electrode 46 can not be less than 3 μm.
The minimum line width of the pixel electrode or the common electrode of the liquid crystal display device of horizontal electric field type is limited by the exposure resolution of an exposure apparatus. The minimum line width can be somewhat reduced by over-etching. However, there is limit as to how much an aperture ratio can be improved by reducing the line width of the pixel electrodes and the common electrodes.